Objective: To advance our knowledge on the mechanism by which hormones control the gene expression of endometrial cells. Approach: A technique to culture rabbit endometrial cells in a chemically defined medium has been developed. Diethylstilbestrol was found to promote cell division, while progesterone had an opposite effect. However, both steroid hormones increase RNA and protein synthesis. Two secretory proteins have been found to be induced by the steroid hormones. The effects of estrogens and progestins upon growth and differentiation will be continued. The hormonal regulation of secretory proteins (identification and purification), growth, cell cycle and hormonal receptors will be studied.